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I Black hole radiation

  1. Jun 24, 2017 #1
    A couple of points I need clarification on.

    Objects outside of the event horizon feel the pull of the black hole - so the closer the object is to the event horizon but still outside of it the more pull the object feels to be sucked into the event horizon? Is that the correct view?

    As far as virtual pair production that leads to Hawking radiation. Does it take place on the event horizon or just outside of it? In either case assuming one of the pair gets sucked into the black hole and the other doesn't, I am not following how energy is lost. So assuming we are talking about virtual photons - one virtual photon goes into the black hole /crosses the event horizon - maybe it was right on the horizon to start with - and the other dashes off. How does this cause the black hole to lose anything? It seems to me it gained a photon and the one that dashed away was never part of the black hole to begin with. So it seems it would look like the black hole has more energy/mass than it began with after such an event - one virtual photon to be exact. How does the black hole provide energy/mass to the photon that was never inside of it to the point the black hole loses energy/mass? I guess the deeper mystery to me is how energy is lost by gravity being just gravity? If you have a huge mass exerting gravity the concept of 'radiation' applied to it would seem to be equivalent to saying that if another much smaller object is brought close to it and starts feeling the force of gravity some of the mass/energy of the large object is lost because there is something close by to feel its gravity - if there was no such nearby object then 'gravity' would not 'lose energy'. Any assistance in clearing this up would be greatly appreciated.
     
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  3. Jun 24, 2017 #2

    phinds

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    Technically yes, but you're overthinking it. As you pass from say a few miles outside the EH of a supermassive BH to a few miles inside, you'll observer practically no change in anything.

    The "virtual pair production" is a hueristic that Hawking came up with because he could not figure out any other way to say in English something that really can only be said with math.

    I suggest a forum search. This topic has been beaten to death HUNDREDS of times here on PF.
     
  4. Jun 24, 2017 #3
    I have done a forum search - did not clarify. I am not sure why your first assumption is that I haven't.

    +++++++
    As far as: "Technically yes, but you're overthinking it. As you pass from say a few miles outside the EH of a supermassive BH to a few miles inside, you'll observer practically no change in anything."

    For one thing as far as I understand the two objects will no longer be able to contact each other. Seems to be a big difference.
    ++++++++
    As far as "The "virtual pair production" is a hueristic that Hawking came up with because he could not figure out any other way to say in English something that really can only be said with math."

    There are a lot of things that can be said with math better than any other way. However that doesn't mean they can't be approximated without math or math that has been simplified.. I see folks like Susskind and others of his reputation and standing using the virtual pair analogy to get their point across to a wider audience than those that know higher end mathematics. So I am not so sure there can't be a better explanation without math or some math that would help me.
    If you posted just to let me know that you couldn't explain anything to me, thanks, you have accomplished your goal - I don't know anymore than when I started after reading your reply. However, I don't universalize your lack of ability to do that to all others on this forum. Perhaps somebody else will make an attempt and after they have I will have the feeling I understand a bit more. I won't be surprised by that but maybe you will. You are always free to post subsequently that it is an extreme trivialization and actually my impression that I know more is a conceit. Your call, your time.
     
  5. Jun 24, 2017 #4

    phinds

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    Sure, only one-way communication is possible, you are right about that. There are other differences as well. For one thing, once you cross the EH you can't get back out again but that doesn't make you feel any different at the time.
     
  6. Jun 25, 2017 #5

    Nugatory

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    One particle in the pair has negative mass/energy and the other has positive mass/energy. The one that ends up inside the black hole is always the negative-energy one while the positive-energy one escapes, so the mass/energy of the black hole is reduced by the interaction.

    You might reasonably ask why it's always the positive energy particle that escapes to infinity, and the answer is that you've just run up against the limitations of the heuristic explanation. You will get some help from here and you can get the real thing from Hawking himself here.
     
    Last edited: Jun 26, 2017
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